It is very difficult, if not impossible, to give a correct account of the national and racial movements which, along with the moral conditions in Judah, called forth Jeremiah's Oracles of judgment in the years immediately following his call in 627-626 B.C. But the following facts are well founded. In or about 625 the Medes were defeated in an attack upon Assyria and their king Phraortes was killed, but at the same time Asshurbanipal died, and his weaker successor was compelled to recognize the virtual independence of Nabopolassar, the Chaldean in Babylon. Cyaxares (624-585), the son of Phraortes, soon after his succession to his father -- say between 624 and 620 -- led a second Median assault upon Assyria and besieged Nineveh, but had to retire because of the onset from the north of the Scythians, the Ashguzai of the Assyrian monuments, probably the Ashkenaz or Ashkunza (?) of the Old Testament. And then it was not for some years that Cyaxares felt himself strong enough by his alliance with Nabopolassar for a third Median invasion of Assyria which culminated in the capture and destruction of Nineveh.
The Assyrians appear to have been in touch with the Ashguzai for over a century and for a shorter time probably in alliance with them; which alliance was the cause of the Scythian advance to the relief of Nineveh from its siege by the Medes circa 724-720 (see Winckler Die Keilinschriften v. das alte Testament, 3rd ed., pp.100 ff.). About the same time must be dated the Scythian advance through Western Asia to the borders of Egypt, which Herodotus (I.103-104, IV.1) reports. Professor N. Schmidt (Enc. Bibl., art. "Scythians") supposes that this advance was due to the same Scythian-Assyrian alliance, in order to preserve the Assyrian territories from the arms of Psamtik of Egypt, who had since 639 been besieging Ashdod; and he holds that this hypothesis explains the absence of any record of violence by the Scythians on their southern campaign, except at Ashkelon. This precarious hypothesis apart, we have the facts that no Biblical chronicler records any invasion of Judah and Benjamin by the Scythians, and yet that the early Oracles of Jeremiah, generally attributed to the alarms which the advance of such barbarian hordes would excite in Judah, do closely fit the Scythians (with a few exceptions that may be due to the prophet's adaptation in 604 of his earlier Oracles to the new enemy out of the north, the Chaldeans).
There, are, however, modern writers who claim that the Oracles in question were originally composed not in view of the Scythian, but of the Chaldean invasion of Palestine. So George Douglas (The Book of Jeremiah, London, Hodder & Stoughton, 1903), who, while assigning Jeremiah's call to 627, relegates the two visions and all the Oracles in the first part of the book to the years following Jehoiakim's accession to the Jewish throne in 608; cp. Winckler, Geschichte Israels, I. pp.112 f. and F. Wilke (Alttestamentliche studien R. Kittel zum 60 Geburtstag dargebracht, 1913), quoted by John Skinner, Prophecy and Religion, pp.42 f. n.2. This would be an easy solution but for the insuperable objections to it that the Oracles in question far more closely fit the Scythian, than the Chaldean, invasion; and that Jer. I.2, as distinctly covers prophecies of Jeremiah in the days of Josiah as v.3 does his prophesying under Jehoiakim.
The date of Nineveh's fall has hitherto been accepted as 607-606 B.C. But in July of this year (1923) Mr. C. J. Gadd described to the British Academy a Babylonian tablet, which dates the fall in the fourteenth year of Nabopolassar's reign in Babylon. This year was 612 B.C., if it be right to reckon the reign from 626-25 B.C.; but as remarked above, p.175, Nabopolassar became in that year officially not king but only viceroy. Dependent as I was on a newspaper summary of Mr. Gadd's lecture I could therefore do no more than offer for the fall of Nineveh the alternative dates, 612 and 606; see above p.175 and compare p.162.